WASHINGTON (AFP) - In a second term, President Barack Obama would face a struggle to put a legacy stamp on a world ever more resistant to US power, as Middle East turmoil rages and emerging states demand their due.

Soon after a second inauguration in January, a fateful moment looms with Iran, with diplomacy aimed at ending its nuclear program either finally getting serious or military action beckoning.

Reverberations from even a limited war with Iran, senior aides confide, would likely consume much of Obama’s replenished diplomatic capital, limiting the foreign policy bandwidth he could use elsewhere.

Crises like Syria’s implosion, the threat from volatile post-Arab Spring societies and territorial tensions in Asia are meanwhile crying out for the presidential attention that has been missing in an election year.

Obama will defend his foreign policy in his final debate with Republican Mitt Romney in Florida on Monday before the too-close-to-call election on November 6.

“The president has kept his word,” spokesman Ben LaBolt told AFP.

“He promised to end the war in Iraq in a responsible way, to take the fight to Al-Qaeda, to put us on a path to end the war in Afghanistan and to restore our alliances around the world.”

In the political bull ring Monday, Obama may seek to puncture Romney rather than define a vision for second term foreign policy. He is sure to remind Americans he has kept them safe after a string of thwarted terror strikes.

Romney will scratch a political wound over the shifting explanations of the attack on the US consulate in Benghazi, which he says is a sign of an unravelling foreign policy.

Re-elected presidents soon become lame ducks at home and often look abroad as the pull of history conjures visions of grand diplomatic gestures. Yet there is little low hanging diplomatic fruit for Obama, with America and Europe hobbled economically and sectarian turmoil splintering the Middle East.

Other nations may also be too boxed in to bargain: leaders from Egypt to China face internal political pressures limiting their room for manoeuvre.

Others, like Russian President Vladimir Putin are not in friendly mood, while states like Yemen pose alarming risks to US security. China is meanwhile bristling at the US turn towards the Pacific, and the intertwined Sino-US economic relationship is often aggravated.

EARLY DREAMS DASHED

A second Obama term would likely show much continuity with the first. Touting the symbolism of his multicultural biography, Obama took power vowing to heal the breach between America and Islam and to tackle perils like climate change.

But intractable problems resisted Obama’s charm and many tilts at history fell flat: a drive for peace between Israel and the Palestinians foundered early, and an open hand to Iran was rebuffed.

So Obama pursued a pragmatic foreign policy of nuance that cheered supporters but annoyed conservatives, who saw a “leading from behind” president on apology tours who emboldened US foes and chided allies.

However, US diplomacy with Moscow and Beijing yielded the toughest-ever sanctions on Iran and US air power helped oust Libya’s Moamar Gaddafi.

A stealth war with drones and special forces in Pakistan, Yemen and elsewhere remoulded the US war on terror, though Obama aides disdain that Bush-era term.

Obama launched a power rebalancing towards Asia to meet the rise of an assertive China and second-tier powers like Indonesia.

In a second term, the Afghan withdrawal in 2014 would complete Obama’s military retrenchment after an era of power-sapping land wars but he would continue to pursue terror suspects into whatever broken land they hide.

“He is a Nobel Peace Prize winner with his own personal kill list,” said Laura Blumenfeld, senior fellow at the German Marshall Fund, painting Obama as a “president who speaks poetry and carries a silencer.”

Obama would also seek new atomic arsenal cuts with Russia and expand a push to keep nuclear material out of the hands of terrorists.

Stung by the Libya crisis, he would need to focus more intensely on the Middle East and North Africa.

“He recognises the Arab Spring is in a very critical time and he’s going to need to be more involved in that than he has been,” said Karl Inderfurth, a former assistant US secretary of state.

“That means reaching out to democratically elected leaders such as President Mohamed Mursi and others to see what role the United States can play in shaping the long term, peaceful democratic transformation of the Arab world.”

Aides say Obama is sincere about working to create a Palestinian state but political estrangement in the region and his own with Israeli leader Benjamin Netanyahu augurs against quick breakthroughs.

A global climate deal would polish Obama’s legacy, but the economic pain it would entail looms as prohibitive after the Great Recession.

Obama may court regions shaking off decades of atrophy, so Myanmar and Southeast Asia could expect more US engagement and he could also trace so far neglected ancestral roots in Africa, aides said.